Blood pressure measuring method, in the conventional way, comprises wrapping a cuff (or manchette) composed of an air-bag, etc. about a portion of a person's body (human body), for example, an arm or leg; temporarily interrupting or closing off blood circulation through an artery by contracting or compressing a portion of a person's body with the air pressure supplied to the cuff; gradually decreasing the air pressure in the cuff while detecting Korotkov's sounds (i.e. frictional sounds between the artery wall and the blood flow) by the use of a sound detector, etc.; and detecting the cuff pressure values at the time when the Korotkov's sounds are produced and begin to disappear for determining a maximal blood pressure (systolic) and a minimal blood pressure (diastolic).
In recent years, an automatic sphygmomanometer which detects Korotkov's sounds and indicates blood pressure by providing a sound collector having a microphone, etc. within the cuff thereof has been developed and widely used to make the blood pressure measurement speedy and easy. Further, such an automatic cuff mechanism as proposed in U.S. Pat. No. 3,935,984 has been developed as a cuff mechanism for the so-called automatic sphygmomanometer to permit mechanically and automatically wrapping a person's arm in a cuff. As a result, the use of the automatic sphygmomanometer has become remarkably easier.
However, the above-mentioned conventional automatic sphygmomanometer involves many problems to be solved. Since it wraps a person's arm or leg with a cuff which is attached to a flexible band, with one end of the band being fixed, and mechanically pulling the other end portion thereof by a combination of a motor, gear, etc., the pulling means is likely to be remarkably complicated in structure and tends to easily get out of order. There is an inherent problem of producing mechanical noise during its operation. Besides, it is still difficult to maintain a suitable pulling force, even if a torque motor is used. Further, there is a danger of presenting an excessive pulling when the pulling means gets out of order.
Moreover, another important or serious problem is that difficulty arises in making a cuff closely contact with the portion of a person's body when the thickness of the portion is not uniform, since the cuff is mechanically and automatically wrapped. In other words, although the portion subjected to a blood pressure measurement is an upper arm of a person as a rule, the thickness of the same is often non-uniform, for example, in case of a sportsman who has unusually developed muscles in that portion. Therefore, in the conventional automatic sphygmomanometer where the band is pulled and compressed almost in a perpendicular direction to the center line of the upper arm, the cuff does not necessarily contact with the upper arm closely and uniformly, thereby a vacant or uncontacted space being formed between the slender part of the upper arm and the cuff. This is the reason why errors appear in blood pressure measuring.